Hi @Tamil Selvan L ,
Per my test, the email can be empty. Please check email in people and groups.
You can update email by following script
Set-SPUser -Identity "i:0#.w|Domain\username" -Email "firstname.lastname@example.org" -Web https://sharepoint-site-url
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.